System and apparatus for enhancing exhaust aftertreatment startup emissions control

ABSTRACT

An aftertreatment system including a method which provides a selective catalytic reduction (SCR) catalyst disposed in an exhaust stream of an engine; determines that an ammonia pre-load condition for the SCR catalyst is present; determines a first amount of ammonia pre-load in response to the ammonia pre-load condition; injects an amount of ammonia or urea into the exhaust stream in response to the first amount of ammonia; and adsorbs a second amount of ammonia onto the SCR catalyst in response to injecting an amount of ammonia or urea, where the second amount of ammonia is either the injected amount of ammonia or an amount of ammonia resulting from hydrolysis from the injected amount of urea.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/045,252 filed on Mar. 10, 2011, which claims the benefit of U.S.Provisional Application No. 61/312,887 filed on Mar. 11, 2010, each ofwhich is incorporated herein by reference for all purposes.

BACKGROUND

The present application generally relates to exhaust aftertreatmentsystems, and more particularly, but not exclusively, to selectivecatalytic reduction (“SCR”) systems. Presently available SCR systemsadsorb ammonia (NH₃) on a catalyst and then react the NH₃ with NO_(x) toreduce the NO_(x) emissions. The NH₃ is typically stored as a lessreactive composition, e.g. urea, and hydrolyzed into NH₃ in the exhaustsystem as required to reduce the NO_(x) emitted by the engine.Immediately after an engine startup event, under certain conditions theexhaust system is not warm enough to sufficiently hydrolyze urea. A lagtime in the ability to deliver NH₃ to the reduction catalyst canincrease emissions of the system. If the NO_(x) reaches the reductioncatalyst and no NH₃ is available, a higher portion of the NO_(x) willslip out of the system as increased emissions.

SUMMARY

One embodiment is a unique method for enhancing exhaust aftertreatmentNO_(x) control after engine startup. Further embodiments, forms,objects, features, advantages, aspects, and benefits shall becomeapparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a system including an exemplarySCR system.

FIG. 2 is a schematic illustration of a system including anotherexemplary SCR system.

FIG. 3 is a flow diagram of a procedure for enhancing exhaustaftertreatment startup emissions control.

FIG. 4 is a diagram illustrating an exemplary controller for enhancingexhaust aftertreatment startup emissions control.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, any alterations and further modificationsin the illustrated embodiments, and any further applications of theprinciples of the invention as illustrated therein as would normallyoccur to one skilled in the art to which the invention relates arecontemplated herein.

With reference to FIG. 1, there is illustrated a system 100 including anengine 110 which is configured to provide rotating mechanical power tosystem 100 and to output exhaust to an exhaust flow path 120. System 100is illustrated schematically and may be a car, truck, bus, boat,recreational vehicle, construction equipment, another type of vehicle,or any device powered by an engine 110. Other embodiments include anengine provided in other applications such as a generator set. Theexhaust output by engine 110 includes NO which is to be reduced using anexhaust aftertreatment system 115.

In one embodiment, exhaust aftertreatment system 115 may include anoxidation catalyst 122 which is in fluid communication with exhaust flowpath 120 and is operable to catalyze oxidation of one or more compoundsin exhaust flowing through exhaust flow path 120, for example, oxidationof NO to NO₂. In another embodiment, exhaust aftertreatment system 115may further include a diesel particulate filter 124 which would be influid communication with exhaust flow path 120 and would be operable toreduce the level of particulates in exhaust flowing through exhaust flowpath 120. In an exemplary embodiment diesel particulate filter 124 is acatalyzed soot filter. Other embodiments utilize other types of dieselparticulate filters.

Exhaust aftertreatment system 115 may include a reductant injector 140and SCR catalyst 130. Reductant injector 140 is supplied with reductantfrom a reductant reservoir 150 and is operable to inject reductant intoexhaust flow path 120. In an exemplary embodiment the reductant is anaqueous solution of urea which decomposes (e.g. by hydrolysis) toprovide NH₃. Reductant injected into exhaust flow path is provided toSCR catalyst 130 which is in flow communication with exhaust flow path120 and is operable to catalyze the reduction of NO_(x).

Exhaust flow path 120, as illustrated schematically in FIG. 1, may beprovided in a variety of physical configurations. In an exemplaryembodiment an exhaust flow path proceeds from the output of aturbocharger of an engine through a conduit to a structure containing anoxidation catalyst and a diesel particulate filter, through a secondconduit to a structure containing an SCR catalyst and through anotherconduit which outlets to the ambient environment. This embodiment mayalso include an ammonia oxidation AMOX catalyst (not shown) at aposition downstream of the SCR catalyst, which is operable to catalyzethe reaction of NH₃ which slips past the SCR catalyst.

Another embodiment is shown in FIG. 2 where positioning of SCR catalyst130 in the exhaust stream is at a vertically higher position thanreductant injector 140 that performs the injecting. The released NH₃ islighter than the ambient gas (air and/or combustion gases) and thepositioning of the SCR catalyst 130 at a position vertically higher thanthe reductant injector 140 can enhance the speed at which the NH₃diffuses into and adsorbs on the SCR catalyst 130, as well as reduce theNH₃ concentration in the vicinity of the injected urea that may remainon the walls of the exhaust flow path 120 and not yet be hydrolyzed. Yetanother embodiment shown in FIG. 1 may include positioning the injector140′ downstream of the SCR catalyst, including positioning the injectordownstream and at a vertically lower position than the SCR catalyst 130.Other embodiments may omit one or more of the foregoing elements,include additional elements, feature alternate elements, and/or featuredifferent arrangements and configurations of elements as would bedetermined by one skilled in the art.

In certain embodiments, system 100 includes a controller 180 whichfunctionally executes certain operations for enhancing startup emissionscontrol of the exhaust aftertreatment system 115. Controller 180 forms aportion of a processing subsystem including one or more computingdevices having memory as well as a number of inputs and outputs forinterfacing with various sensors and devices of system 100. Controller180 can be an electronic circuit comprised of one or more components,including digital circuitry, analog circuitry, or both. Controller 180may be a single device or a distributed device. Controller 180 mayinclude one or more control algorithms defined by operating logic in theform of software instructions, hardware instructions, firmwareinstructions, dedicated hardware, or the like.

In one embodiment, controller 180 is of a programmable microcontrollersolid-state integrated circuit device including memory and one or morecentral processing units. The memory of controller 180 can be comprisedof one or more components and can be of any volatile or nonvolatiletype, including solid-state, optical media, magnetic media, combinationsof these, or other types of memory. Controller 180 can include signalconditioners, signal format converters (such as analog-to-digital anddigital-to-analog converters), limiters, clamps, filters, and the likeas needed to perform various control and regulation operations describedherein. Controller 180, in an exemplary embodiment, may be a type ofcontroller sometimes referred to as an electronic or engine controlmodule (ECM), electronic or engine control unit (ECU) or the like, thatis directed to the regulation and control of engine operation.Alternatively, controller 180 may be dedicated to the control of justthe operations described herein or to a subset of controlled aspects ofsystem 100.

In certain embodiments, the controller 180 includes one or more modulesstructured to functionally execute the operations of the controller 180.The description herein including modules emphasizes the structuralindependence of the aspects of the controller, and illustrates onegrouping of operations and responsibilities of the controller 180. Othergroupings that execute similar overall operations are understood withinthe scope of the present application. Modules may be implemented inhardware and/or software on computer readable medium, and modules may bedistributed across various hardware or software components.

Controller 180 is in operative interconnection with various elements ofsystem 100 as illustrated in FIG. 1 with dashed lines extending betweencontroller 180 and various elements of system 100. These operativeinterconnections may be implemented in a variety of forms, for example,through input/output interfaces coupled via wiring harnesses, adatalink, a hardwire or wireless network and/or a lookup from a memorylocation. In other instances all or a portion of the operativeinterconnection between controller 180 and an element of system 100 maybe virtual. For example, a virtual input indicative of an operatingparameter may be provided by a model implemented by controller 180 or byanother controller which models an operating parameter based upon otherinformation. The system 100 may include interconnections with thecontroller 180 that are not shown, and alternatively or additionallysome of the illustrated interconnections may not be present.

Controller 180 is in operative communication with temperature sensor 160which provides controller 180 with information indicative of thetemperature of the exhaust flow path 120 in the region of the injector140. The controller 180 may further be in operative communication with atemperature sensor (not shown) that provides ambient air temperature.Controller 180 is in operative communication with a temperaturedeterminer 170 which provides controller 180 with information indicativeof the temperature of SCR catalyst 130. In an exemplary embodiment thetemperature determiner 170 provides the information indicative of thetemperature of SCR catalyst 130 utilizing temperature sensors (notshown) upstream and/or downstream of the SCR catalyst 130 in combinationwith a model that uses a weighted average of information from thetemperature sensors. In other embodiments, the temperature determiner170 utilizes any models and/or measured parameters in the system 100 todetermine the information indicative of the temperature of SCR catalyst130.

In another embodiment, controller 180 may be in operative communicationwith NO_(x) sensor 195 which provides controller 180 with informationindicative of the level of NO_(x) output from SCR catalyst 130. In anexemplary embodiment NO_(x) sensor 195 is a physical sensor which is influid communication with exhaust flow path 120. Other embodiments mayprovide information indicative of the level of NO_(x) output from SCRcatalyst 130 utilizing a greater number of sensors, different types ofsensors or information available from an engine controller (not shown).In other embodiments, controller 180 may be part of the enginecontroller or may have a separate component pertaining to a NO_(x)output sensor.

The controller may also be in operative communication with a virtualNO_(x) sensor which provides the controller with information indicativeof the level of NO_(x) input to the SCR catalyst using a model basedupon operating conditions of the engine, for example, engine load,engine fueling, exhaust temperature and/or other parameters. In otherembodiments, an upstream NO_(x) sensor (not shown) is in fluidcommunication with exhaust flow path 120 and is located upstream fromSCR catalyst 130.

During operation controller 180 uses the information indicative of thelevel of NO_(x) provided to SCR catalyst 130 along with information fromsensors 160, 170, 195 to determine the amount or rate of reductant to beinjected by reductant injector 140. Controller 180 is in operativecommunication with reductant injector 140 and can command reductantinjector 140 to inject a selected amount of reductant or to injectreductant at a selected rate. In an exemplary embodiment controller 180commands reductant injection that is determined to maximize thecatalytic reduction of NO_(x) by SCR catalyst 130, to maximize NH₃storage by SCR catalyst 130, to reduce NO_(x) with the SCR catalyst toprescribed levels, to minimize the slip of NH₃ past SCR catalyst 130,and/or to ensure slip of NH₃ past the AMOX is at acceptable levels. Inother embodiments, controller 180 commands reductant injection todifferently balance these parameters or to account for additional ordifferent parameters.

Referencing FIG. 4, an apparatus includes a controller 180 with variouscomponents illustrated as representative modules, inputs, outputs, andintermediate data parameters. Module 410 is an NH₃ pre-loading modulestructured to determine if an NH₃ pre-load condition 415 for an SCRcatalyst is present. The NH₃ pre-loading module 410 may be structured todetermine if the NH₃ pre-load condition 415 for the SCR catalyst ispresent using one or more of the following determinations: (1)determining that an ambient temperature 402 is above a urea hydrolysisthreshold 412 and therefore injected urea will be sufficientlyhydrolyzed; (2) determining that an ambient temperature 402 is below acold start threshold 414 and therefore suggesting potential for NO_(x)emission on a subsequent engine start before system temperature is ableto achieve urea hydrolysis temperature 427; (3) determining that an NH₃storage amount 406 on the SCR catalyst is below a storage neededthreshold 416 and additional NH₃ storage is desirable; or (4)determining that a current SCR catalyst temperature 404 is within an NH₃storage temperature range 418 and therefore injected and hydrolyzed ureawill result in additional NH₃ stored on the SCR catalyst.

Module 420 is an NH₃ requirements module 420 structured to determine afirst amount of NH₃ pre-load 450 in response to the NH₃ pre-loadcondition 415. The NH₃ requirements module 420 may be structured todetermine a first amount of NH₃ pre-load 450 using a quantifyingoperation such as one of the following: (1) determining a currentavailable NH₃ storage capacity 422 of the SCR catalyst at a current SCRcatalyst temperature 404; (2) modeling a final temperature of the SCRcatalyst 423 that will be present after an amount of injected ureahydrolyzes into NH₃ and then determining a final available storagecapacity 422 a of the SCR catalyst that will be available at the finaltemperature of the SCR catalyst 423; (3) determining an amount of NH₃421 selected such that if the engine is cold soaked to a current ambienttemperature 402, a cold start NO_(x) converted 425 (i.e. the amount ofNO_(x) converted by the amount of NH₃ 421 in a subsequent cold startevent until a urea hydrolysis temperature 427 is reached) will be greatenough such that a cold start NO_(x) emitted 425 (the incremental amountof NO_(x) emitted due to the cold start event) is less than a thresholdamount of NO_(x) 426 during the subsequent cold start event; or (4)determining an amount of NH₃ 421 selected such that determining anamount of NH₃ 421 selected such that if the engine is cold soaked to acurrent ambient temperature 402, the amount of NO_(x) converted by atotal amount of NH₃ 428 on the SCR catalyst (i.e. including the amountof NH₃ 421 added to an initial amount of NH₃ 429) in a subsequent coldstart event will be great enough such that a cold start NO_(x) emitted425 (the incremental amount of NO_(x) emitted due to the cold startevent) is less than the threshold amount of NO_(x) 426 during thesubsequent cold start event.

The NH₃ requirements module 420 may be further structured to determinethe first amount of NH₃ pre-load 450 using an iterative operation whichupdates the first amount of NH₃ pre-load 450 in response to the NH₃pre-load condition 415 followed by subsequent determinations of anamount of NH₃ 421 in response to subsequent conditions. For example, andwithout limitation, a change in the ambient temperature 402 may changethe amount of NH₃ 421 desired to achieve the target cold start NO_(x)emitted 425. The described adjustments are exemplary, and any otheradjustments to updating conditions are contemplated herein. Module 420may use any combination of determinations for pre-load conditions orquantifying operations for determining a first amount of NH₃ pre-load450 during the iterations. The iterative determination of the firstamount of NH3 pre-load 450, in addition to incremental addition of theamount of NH3 421 instead of injecting the entire amount of NH3 421 atonce, allows for adjustments in the NH₃ pre-load condition on the SCRcatalyst in response to situations such as a premature engine start orambient temperature changes, thereby limiting the presence ofun-adsorbed NH3 or urea in the exhaust flow path 120 which may cause NH₃slip if an engine start occurs before the system reaches equilibrium.

Module 430 is an injector command module structured to provide a NO_(x)reductant injection signal 435 in response to the first amount of NH₃pre-load 450. The injector command module 430 may also be structured toprovide a NO_(x) reductant injection signal 435 in response to theengine being shut down 405 or in response to an engine eminent shutdown405 a condition. In one embodiment, an engine shutdown is imminent(e.g., without limitation, the keyswitch is off and the engine speed isfalling) and injector command module 430 responds by injecting at leastpart of the amount of NH₃ 421 or urea into the exhaust stream before theengine shutdown is completed (e.g. while the engine control module stillhas power during the power down sequence after the keyswitch is off).This embodiment may also further include injecting the amount of NH₃ 421or urea into the exhaust stream over a period of time.

The injector command module 430 may be further structured to provide aNO_(x) reductant injection signal 435 such that an NH₃ concentrationvalue 442 in the exhaust stream does not exceed NH₃ threshold 444—forexample by injecting small portions of the amount of NH₃ 421 over anextended period such that the NH₃ concentration value 442 is neverhigher than the NH₃ threshold 444. The operations of the injectorcommand module 430 may be coordinated by the NH₃ scheduling module 440.The NH₃ scheduling module 440 is structured to determine a current NH₃concentration 442. NH₃ scheduling module 440 is structured to monitor acurrent NH₃ concentration 442 in relation to the NH₃ threshold 444. TheNH₃ threshold 444 may be an emissions limit 446 or an amicability limit448. In one embodiment, NH₃ threshold 444 may be determined based on anemission limit 446 to reduce the release of excess NH₃ to theenvironment. When excess NH₃ slips through the SCR catalyst withoutreacting with the NO_(x) emissions and is exhausted by the system, thecondition is called NH₃ slip. The NH₃ slip limit may be determined byregulatory limits, amicability limits, or by other concerns understoodin the art.

The schematic flow diagram and related description which followsprovides an illustrative embodiment of performing procedures forenhancing exhaust aftertreatment startup emissions control. Operationsillustrated are understood to be exemplary only, and operations may becombined or divided, and added or removed, as well as re-ordered inwhole or part, unless stated explicitly to the contrary herein. Certainoperations illustrated may be implemented by a computer executing acomputer program product on a computer readable medium, where thecomputer program product comprises instructions causing the computer toexecute one or more of the operations, or to issue commands to otherdevices to execute one or more of the operations.

Referencing FIG. 3, a process 300 includes operation 310 to provide aselective catalytic reduction (SCR) system as part of an exhaust streamof an engine. The procedure 300 further includes conditional 320 todetermine if an NH₃ pre-load condition for the SCR catalyst is present.The NH₃ pre-load conditions include conditions of the system thatindicate circumstances for pre-loading the SCR catalyst with reductantto accommodate a potential for a higher level of ability to convertNO_(x) produced during certain engine operations. In one embodiment, theengine operation includes an engine shutdown and then a cold restart.The potential for a higher level of ability to convert NO_(x) can beachieved by pre-loading the SCR catalyst with a reductant such as NH₃.In addition, the temperature may affect the pre-load capabilities suchas the ability for urea to hydrolyze, the amount of NO_(x) that may beproduced during a system warm up, and the ability to store NH₃ in theSCR catalyst in preparation for a higher level of ability to processexhaust gases based on the amount of NH₃ already stored and thetemperature.

In various embodiments, the conditional 320 includes one or more of thefollowing operations: determining that an ambient temperature is above aurea hydrolysis threshold; determining that an ambient temperature isbelow a cold start threshold; determining that an NH₃ storage amount onthe SCR catalyst is below a storage needed threshold; or determiningthat a current SCR temperature is within an NH₃ storage temperaturerange. Temperature can be a factor in the various chemical reactions ofthese processes including the ability of the catalyst to either store ormaintain an acceptable level of NH₃ and the rate at which injected ureahydrolyzes and NH₃ adsorbs onto the SCR catalyst. The amount of NH₃stored in an SCR catalyst correlates to the amount of NO_(x) that can bereadily converted. To handle an engine operation causing a higher levelof NO_(x) at a time when rapid urea hydrolysis is not possible, an SCRcatalyst with a corresponding higher level of NH₃ is able to convert agreater portion of the NO_(x). Ensuring a predefined level of NH₃ isavailable on the catalyst may aid in reducing the amount of unconvertedNO_(x) leaving the emissions system.

The urea hydrolysis threshold may be a temperature value that is atleast 20° C. or at least 0° C. The urea hydrolysis threshold temperaturemay also be a temperature selected such that a sufficient amount of NH₃hydrolyzes from the injected amount of urea before the temperature ofthe exhaust pipe falls below 20° C. As the temperature of a system dropsfollowing an engine operation such as a shutdown, the ability of theurea to hydrolyze may be reduced below a predetermined threshold.Determining the operating conditions under which the system has theability to utilize urea for NO_(x) conversion should include selecting atemperature that maintains adequate hydrolysis. In one embodiment, theurea should be injected to allow hydrolysis before the temperature ofthe system falls to a level where hydrolysis will not be adequate toproduce sufficient NH₃ for pre-loading an SCR catalyst. In analternative, the urea hydrolysis threshold temperature may be atemperature selected such that a sufficient amount of NH₃ hydrolyzesfrom the injected amount of urea before the temperature of the exhaustpipe falls below a hydrolysis temperature limit.

A cold start condition where the engine has ceased operation and hascooled below normal operating temperatures may create a situation uponrestart where a level of NO_(x) produced by the ‘cold’ engine is emittedbecause the temperature of the aftertreatment system is below atemperature necessary for NH₃ production. To limit the amount of NO_(x)emitted during cold starts, a cold start threshold may trigger apre-load condition allowing an increased level of NH₃ for NO_(x)conversion as an engine goes through a cold start. The colder an enginegets, the longer the engine takes to warm up to reach a urea hydrolysistemperature threshold. The longer the engine takes to warm up the moreopportunity for NO_(x) to pass through the emission system unconverted.A pre-loaded catalyst may contain sufficient NH₃ to convert a higherlevel of the NO_(x). The cold start threshold may be 35° C. or atemperature selected such that, if the engine is cold soaked to theselected cold start threshold, a related threshold amount of NO_(x) maybe emitted by the engine during a subsequent engine start before a ureahydrolysis temperature is reached in the exhaust stream.

If conditional 320 in FIG. 3 returns a positive response, the procedure300 continues with operation 330 to determine a first amount of NH₃pre-load in response to the NH₃ pre-load condition. The operation 330includes one or more of the following determinations: (1) determining acurrent available storage capacity of the SCR catalyst at a current SCRcatalyst temperature, and determining the first amount of NH₃ pre-loadin response to determining a fraction of the first amount of NH₃pre-load that will be adsorbed onto the SCR catalyst; (2) modeling afinal temperature of the SCR catalyst that will be present after theinjected urea hydrolyzes into NH₃ then determining a final availablestorage capacity of the SCR catalyst that will be available at the finaltemperature of the SCR catalyst; (3) determining an amount of NH₃selected such that if the engine is cold soaked to a current ambienttemperature, enough NO_(x) will be converted by the amount of NH₃ duringa subsequent engine start that a threshold amount of NO_(x) will not beemitted downstream of the SCR catalyst during a subsequent engine startbefore a urea hydrolysis temperature will be reached in the exhauststream; or (4) determining an amount of NH₃ such that if the engine iscold soaked to a current ambient temperature, enough NO_(x) will beconverted by a total amount of NH₃ stored on the SCR catalyst (includinginitially stored NH₃ plus the first amount of NH₃ pre-load) during asubsequent engine start that a threshold amount of NO_(x) will not beemitted downstream of the SCR catalyst before a urea hydrolysistemperature is reached in the exhaust stream. By limiting the amount ofNO_(x) emitted during an engine start up, the over all emissions will bereduced. Pre-loading the catalyst with NH₃ allows for the conversion ofa related amount of NO_(x) by reducing the amount of NO_(x) emittedduring start up and before the exhaust system reaches a temperature thatagain promotes the reactions necessary to convert NO_(x). By limitingthis initial NO_(x) emission, the impact to the system of initialemissions on a cold start is reduced.

The procedure 300 further includes operation 340 to inject an amount ofNH₃ or urea into the exhaust stream in response to the first amount ofNH₃ pre-load. In one embodiment, the injected amount of NH₃ may besubstantially all the NH₃ necessary to satisfy the pre-load amountdetermination. In another embodiment, the injected amount may consist ofa partial amount of NH₃ pre-load followed by a return to operation 330to determine a second amount of NH₃ pre-load based on a subsequent setof conditions and another partial amount of NH₃ pre-load injected duringa subsequent injection under operation 340. Amounts of NH₃ pre-load aredetermined based on predicted performance considered during operation330. In situations where an amount of NH₃ pre-load is determined andinjected based on predicted conditions such as a cold soak, there is apotential for excess NH₃ when the engine is restarted before thepredicted condition is reached which may cause NH₃ slip. By injecting apartial amount of NH₃ and returning to operation 330, incrementalamounts of NH₃ are injected as time progresses rather than a singleinjection of the initially determined pre-load amount. Incrementalinjections of NH3 reduce the degree of prediction necessary and providefor a more accurate pre-load achievement.

Operation 340 may include injecting an amount of NH₃ or urea after theengine is shut down. Operation 340 is shown to be followed by operation350 where a second amount of NH₃ is adsorbed onto the SCR catalyst inresponse to the injecting. The second amount of NH₃ can be the injectedamount of NH₃, an amount of NH₃ resulting from hydrolysis from theinjected amount of urea or a combination of the two.

As is evident from the figures and text presented above, a variety ofembodiments according to the present invention are contemplated.

One embodiment is a method including: (1) providing a selectivecatalytic reduction (SCR) catalyst disposed in an exhaust stream of anengine; (2) determining that an NH₃ pre-load condition for the SCRcatalyst is present; (3) determining a first amount of NH₃ pre-load inresponse to the NH₃ pre-load condition; (4) injecting an amount of NH₃or urea into the exhaust stream in response to the first amount of NH₃;and (5) adsorbing a second amount of NH₃ onto the SCR catalyst inresponse to the injecting. The second amount of NH₃ can be the injectedamount of NH₃, an amount of NH₃ resulting from hydrolysis from theinjected amount of urea or a combination.

Other features of this embodiment may include injecting an amount of NH₃or urea after the engine is shut down. Further, determining that an NH₃pre-load condition for the SCR catalyst is present includes at least oneof the following operations: determining that an ambient temperature isabove a urea hydrolysis threshold; determining that an ambienttemperature is below a cold start threshold; determining that an NH₃storage amount on the SCR catalyst is below a storage needed threshold;or determining that a current SCR temperature is within an NH₃ storagetemperature range.

Other features of this embodiment may include the urea hydrolysisthreshold being a temperature value selected as being at least 20° C. orat least 0° C. The urea hydrolysis threshold temperature may also besuch that a sufficient amount of NH₃ hydrolyzes from the injected amountof urea before a temperature of the exhaust pipe falls below 20° C. Inan alternative, the urea hydrolysis threshold temperature may be suchthat a sufficient amount of NH₃ hydrolyzes from the injected amount ofurea before a temperature of the exhaust pipe falls below a hydrolysistemperature limit.

Further features of this embodiment may include the cold start thresholdbeing a temperature value selected as being 35° C. or a temperatureselected such that, if the engine is cold soaked to the cold startthreshold, a threshold amount of NO_(x) will be emitted by the engineduring a subsequent engine start before a urea hydrolysis temperaturewill be reached in the exhaust stream.

Another feature of this embodiment may include positioning the SCRcatalyst in the exhaust stream at a vertically higher position than aninjector that performs the injecting. Yet another feature of thisembodiment may include positioning the injector downstream of the SCRcatalyst.

A further feature of this embodiment may include determining the firstamount of NH₃ pre-load by a quantifying operation selected from one ofthe following: (1) determining a current available storage capacity ofthe SCR catalyst at a current SCR catalyst temperature; (2) modeling afinal temperature of the SCR catalyst that will be present after theinjected urea hydrolyzes into NH₃ then determining a final availablestorage capacity of the SCR catalyst that will be available at the finaltemperature of the SCR catalyst; (3) determining an amount of NH₃selected such that if the engine is cold soaked to a current ambienttemperature, enough NO_(x) will be converted by the amount of NH₃ duringa subsequent engine start that a threshold amount of NO_(x) will not beemitted downstream of the SCR catalyst during a subsequent engine startbefore a urea hydrolysis temperature will be reached in the exhauststream; or (4) determining an amount of NH₃ selected such that if theengine is cold soaked to a current ambient temperature, enough NO_(x)will be converted by a total amount of NH₃ stored on the SCR catalystduring a subsequent engine start that a threshold amount of NO_(x) willnot be emitted downstream of the SCR catalyst during a subsequent enginestart before a urea hydrolysis temperature will be reached in theexhaust stream where the total amount of NH₃ includes the amount of NH₃plus an initially stored amount of NH₃.

This embodiment may further include determining that an engine shutdownis imminent and injecting at least part of the NH₃ or urea into theexhaust stream before the engine shutdown is completed. This embodimentmay also further include injecting the NH₃ or urea into the exhauststream over a period of time such that an NH₃ concentration value in theexhaust stream does not exceed an NH₃ threshold. Still further, the NH₃threshold may include an emissions limit or an amicability limit.

Another embodiment may include a system with an engine fluidly coupledto an exhaust stream; a selective catalytic reduction (SCR) catalystdisposed in the exhaust stream; a NO_(x) reductant injectoroperationally coupled to the exhaust stream and fluidly coupled to oneof an NH₃ source and a urea source; a temperature sensor structured todetermine a temperature corresponding to an ambient air temperature; atemperature determiner, comprising one of a sensor and a model,structured to determine a temperature corresponding to an SCR catalysttemperature; and a controller. The controller is structured to determinethat an NH₃ pre-load condition for the SCR catalyst is present;determine a first amount of NH₃ pre-load in response to the NH₃ pre-loadcondition; and command the injector to inject an amount of NH₃ or ureainto the exhaust stream in response to the first amount of NH₃, suchthat the SCR catalyst adsorbs a second amount of NH₃ in response to theinjecting, where the second amount of NH₃ is either the injected amountof NH₃ or an amount of NH₃ resulting from hydrolysis from the injectedamount of urea.

Further features of this embodiment may include an SCR catalyst in theexhaust stream positioned at a vertically higher position than theinjector and, in addition, an injector positioned downstream of the SCRcatalyst.

Still another embodiment is an apparatus including an NH₃ pre-loadingmodule structured to determine that an NH₃ pre-load condition for an SCRcatalyst is present where the SCR catalyst is disposed in an exhauststream of an engine; an NH₃ requirements module structured to determinea first amount of NH₃ pre-load in response to the NH₃ pre-loadcondition; an injector command module structured to provide a NO_(x)reductant injection signal in response to the first amount of NH₃.

A further feature of this embodiment includes the injector commandmodule being structured to provide a NO_(x) reductant injection signalin response to the engine being shut down. Another feature may includethe NH₃ pre-loading module being structured to determine that the NH₃pre-load condition for the SCR catalyst is present by one of thefollowing determinations: (1) determining that an ambient temperature isabove a urea hydrolysis threshold; (2) determining that an ambienttemperature is below a cold start threshold; (3) determining that an NH₃storage amount on the SCR catalyst is below a storage needed threshold;or (4) determining that a current SCR temperature is within an NH₃storage temperature range.

A further feature of this embodiment may include the NH₃ requirementsmodule being further structured to determine a first amount of NH₃pre-load by a quantifying operation selected from one of the following:(1) determining a current available storage capacity of the SCR catalystat a current SCR catalyst temperature; (2) modeling a final temperatureof the SCR catalyst that will be present after the injected ureahydrolyzes into NH₃ then determining a final available storage capacityof the SCR catalyst that will be available at the final temperature ofthe SCR catalyst; (3) determining an amount of NH₃ selected such that ifthe engine is cold soaked to a current ambient temperature, enoughNO_(x) will be converted by the amount of NH₃ during a subsequent enginestart that a threshold amount of NO_(x) will not be emitted downstreamof the SCR catalyst during a subsequent engine start before a ureahydrolysis temperature will be reached in the exhaust stream; or (4)determining an amount of NH₃ selected such that if the engine is coldsoaked to a current ambient temperature, enough NO_(x) will be convertedby a total amount of NH₃ stored on the SCR catalyst during a subsequentengine start that a threshold amount of NO_(x) will not be emitteddownstream of the SCR catalyst during a subsequent engine start before aurea hydrolysis temperature will be reached in the exhaust stream wherethe total amount of NH₃ includes the amount of NH₃ plus an initiallystored amount of NH₃.

A further feature of this embodiment includes the NH₃ scheduling modulewhich is structured to determine a current NH₃ concentration value andthe injector command module which is further structured to provide theNO_(x) reductant injection signal such that an NH₃ concentration valuein the exhaust stream does not exceed an NH₃ threshold. Yet anotherfeature includes the NH₃ threshold being an emissions limit or anamicability limit.

Certain exemplary embodiments are described following.

An exemplary set of embodiments is a method, including providing aselective catalytic reduction (SCR) catalyst disposed in an exhauststream of an engine, determining that an ammonia (NH₃) pre-loadcondition for the SCR catalyst is present, and determining a firstamount of NH₃ pre-load in response to the NH₃ pre-load condition. Themethod further includes injecting an amount of reductant into theexhaust stream in response to the first amount of NH₃ pre-load, wherethe injecting is performed after the engine is shut down. Exemplaryembodiments of the method further include adsorbing a second amount ofNH₃ onto the SCR catalyst in response to the injecting. The reductantmay be NH₃, where the second amount of NH₃ comprises the injected amountof NH₃. The reductant may alternatively be urea, where the second amountof NH₃ includes an amount of NH₃ resulting from hydrolysis from theinjected amount of urea.

Determining that the NH₃ pre-load condition for the SCR catalyst ispresent includes, in certain embodiments, determining that an ambienttemperature is above a urea hydrolysis threshold. Exemplary ureahydrolysis threshold temperatures include at least 20° C., at least 0°C., a temperature selected such that a sufficient amount of NH₃hydrolyzes from the injected amount of urea before a temperature of theexhaust pipe falls below 20° C., and/or a temperature selected such thata sufficient amount of NH₃ hydrolyzes from the injected amount of ureabefore a temperature of the exhaust pipe falls below a hydrolysistemperature limit. The temperature such that a sufficient of amount ofNH₃ hydrolyzes from the injected amount of urea may be determined fromthe acceptable amount of NH₃ that is to available for adsorption on theSCR catalyst, and/or from the acceptable amount of urea that remains inthe exhaust conduit until a subsequent engine start or ambient warm-up.

Exemplary embodiments of the method further include determining that anNH₃ pre-load condition for the SCR catalyst is present by determiningthat an ambient temperature is below a cold start threshold. Exemplarycold start threshold values include 35° C., and/or a temperatureselected such that, if the engine is cold soaked to the cold startthreshold, a threshold amount of NO_(x) will be emitted by the engineduring a subsequent engine start before a urea hydrolysis temperaturewill be reached in the exhaust stream. The threshold amount of NO_(x)that can be emitted by the engine during a subsequent engine start maybe selected according to acceptable emissions values or according toother considerations.

Another exemplary embodiment of the method includes determining that anNH₃ pre-load condition for the SCR catalyst is present by determiningthat an NH₃ storage amount on the SCR catalyst is below a storage neededthreshold. Yet another exemplary embodiment of the method includesdetermining that the NH₃ pre-load condition for the SCR catalyst ispresent by determining that a current SCR temperature is within an NH₃storage temperature range. Yet another exemplary embodiment of themethod includes positioning the SCR catalyst in the exhaust stream at avertically higher position than an injector that performs the injecting,and may further include positioning the injector downstream of the SCRcatalyst. The injector positioned downstream of the SCR catalyst may bea second (or additional) reductant injector present in the system.

Yet another exemplary set of embodiments is a method, includingoperating an internal combustion engine, and treating an exhaust streamof the engine with a selective catalytic reduction (SCR) catalyst. Themethod further includes shutting down the engine, and in response to theshutting down the engine, determining that an ammonia (NH₃) pre-loadcondition for the SCR catalyst is present, determining a first amount ofNH₃ pre-load in response to the NH₃ pre-load condition, and injecting anamount of urea into the exhaust stream in response to the first amountof NH₃ pre-load. Further embodiments include determining the firstamount of NH₃ pre-load by determining a current available storagecapacity of the SCR catalyst at a current SCR catalyst temperature; bymodeling a final temperature of the SCR catalyst that will be presentafter the injected urea hydrolyzes into NH₃, and determining a finalavailable storage capacity of the SCR catalyst that will be available atthe final temperature of the SCR catalyst; by determining an amount ofNH₃ selected such that if the engine is cold soaked to a current ambienttemperature, enough NO_(x) will be converted by the amount of NH₃ duringa subsequent engine start that a threshold amount of NO_(x) will not beemitted downstream of the SCR catalyst during a subsequent engine startbefore a urea hydrolysis temperature will be reached in the exhauststream; and/or by determining an amount of NH₃ selected such that if theengine is cold soaked to a current ambient temperature, enough NO_(x)will be converted by a total amount of NH₃ stored on the SCR catalystduring a subsequent engine start that a threshold amount of NO_(x) willnot be emitted downstream of the SCR catalyst during a subsequent enginestart before a urea hydrolysis temperature will be reached in theexhaust stream, wherein the total amount of NH₃ comprises the amount ofNH₃ plus an initially stored amount of NH₃.

Additional or alternative embodiments include determining that theshutting down the engine is imminent, and injecting at least part of theurea into the exhaust stream before the shutting down the engine iscompleted. Yet another exemplary embodiment includes injecting the ureainto the exhaust stream over a period of time such that an NH₃concentration value in the exhaust stream does not exceed an NH₃threshold. A further embodiment includes determining the NH₃ thresholdas one of an emissions limit and an amicability limit.

Yet another exemplary set of embodiments is a system, including anengine fluidly coupled to an exhaust stream, a selective catalyticreduction (SCR) catalyst disposed in the exhaust stream, and a NO_(x)reductant injector operationally coupled to the exhaust stream andfluidly coupled to one of an ammonia (NH₃) source and a urea source. Thesystem further includes a controller structured to interpret an SCRcatalyst temperature and an ambient temperature, to determine that anNH₃ pre-load condition for the SCR catalyst is present in response tothe ambient temperature, to determine a first amount of NH₃ pre-load inresponse to the NH₃ pre-load condition and the SCR catalyst temperature,and to command the injector to inject an amount of urea into the exhauststream in response to the first amount of NH₃ pre-load.

In certain embodiments, the controller is further structured todetermine that the NH₃ pre-load condition is present in response todetermining that the ambient temperature is below a cold startthreshold. Exemplary cold start threshold values include 35° C., and/ora temperature selected such that, if the engine is cold soaked to thecold start threshold, a threshold amount of NO_(x) will be emitted bythe engine during a subsequent engine start before a urea hydrolysistemperature will be reached in the exhaust stream.

In certain embodiments, the controller is further structured todetermine that the NH₃ pre-load condition is present in response todetermining that the ambient temperature is above a urea hydrolysisthreshold. Exemplary urea hydrolysis threshold values include at least20° C., at least 0° C., a temperature selected such that a sufficientamount of NH₃ hydrolyzes from the injected amount of urea before atemperature of the exhaust pipe falls below 20° C., and/or a temperatureselected such that a sufficient amount of NH₃ hydrolyzes from theinjected amount of urea before a temperature of the exhaust pipe fallsbelow a hydrolysis temperature limit. The hydrolysis temperature limitmay be a temperature selected such that the hydrolysis of ureaprogresses below a threshold rate at or below the hydrolysistemperature—for example where the amount of urea remaining in theexhaust will, on average, exceed an acceptable level at a subsequentengine start event that occurs at an average estimated later time.

An exemplary embodiment of the system includes the SCR catalyst in theexhaust stream positioned at a vertically higher position than theinjector. A further exemplary embodiment includes the injectorpositioned downstream of the SCR catalyst.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly certain exemplary embodiments have been shown and described andthat all changes and modifications that come within the spirit of theinventions are desired to be protected. In reading the claims, it isintended that when words such as “a,” “an,” “at least one,” or “at leastone portion” are used there is no intention to limit the claim to onlyone item unless specifically stated to the contrary in the claim. Whenthe language “at least a portion” and/or “a portion” is used the itemcan include a portion and/or the entire item unless specifically statedto the contrary.

What is claimed is:
 1. A system, comprising: an engine fluidly coupled to an exhaust stream; a selective catalytic reduction (SCR) catalyst disposed in the exhaust stream; a NO_(x) reductant injector operationally coupled to the exhaust stream and fluidly coupled to one of an ammonia (NH₃) source and a urea source; a controller operably connected to the NO_(x) reductant injector and configured to: interpret an SCR catalyst temperature and an ambient temperature; determine that an NH₃ pre-load condition for the SCR catalyst is present in response to the ambient temperature; determine a first amount of NH₃ pre-load in response to the NH₃ pre-load condition and the SCR catalyst temperature; determine that the NH₃ pre-load condition is present in response to the ambient temperature being below a cold start threshold; and command the injector to inject an amount of urea into the exhaust stream in response to the first amount of NH₃ pre-load.
 2. The system of claim 1, wherein the cold start threshold comprises a temperature value selected from the temperature values comprising: 35° C.; and a temperature selected such that, if the engine is cold soaked to the cold start threshold, a threshold amount of NO_(x) will be emitted by the engine during a subsequent engine start before a urea hydrolysis temperature will be reached in the exhaust stream.
 3. The system of claim 1, wherein the controller is further structured to determine that the NH₃ pre-load condition is present in response to the ambient temperature being above a urea hydrolysis threshold.
 4. The system of claim 3, wherein the urea hydrolysis threshold comprises a temperature value selected from the temperature values comprising: at least 20° C.; at least 0° C.; a temperature selected such that a sufficient amount of NH₃ hydrolyzes from the injected amount of urea before a temperature of an exhaust pipe falls below 20° C.; and a temperature selected such that a sufficient amount of NH₃ hydrolyzes from the injected amount of urea before a temperature of the exhaust pipe falls below a hydrolysis temperature limit.
 5. The system of claim 1, wherein the SCR catalyst in the exhaust stream is positioned at a vertically higher position than the injector.
 6. A system, comprising: an engine fluidly coupled to an exhaust stream; a selective catalytic reduction (SCR) catalyst disposed in the exhaust stream; a NO_(x) reductant injector operationally coupled to the exhaust stream and fluidly coupled to one of an ammonia (NH₃) source and a urea source, wherein the SCR catalyst in the exhaust stream is positioned at a vertically higher position than the injector and the injector is positioned downstream of the SCR catalyst; a controller operably connected to the NO_(x) reductant injector and configured to: interpret an SCR catalyst temperature and an ambient temperature; determine that an NH₃ pre-load condition for the SCR catalyst is present in response to the ambient temperature; determine a first amount of NH₃ pre-load in response to the NH₃ pre-load condition and the SCR catalyst temperature; and command the injector to inject an amount of urea into the exhaust stream in response to the first amount of NH₃ pre-load.
 7. An apparatus, comprising: an electronic controller operably connected to a plurality of sensors associated with an exhaust aftertreatment system that receives an exhaust stream of an engine, the exhaust aftertreatment system including an SCR catalyst and a reductant injector, wherein the controller is operably connected to the reductant injector, the controller including: an ammonia (NH₃) pre-loading module configured to determine that an NH₃ pre-load condition for the SCR catalyst is present; an NH₃ requirements module configured to determine a first amount of NH₃ pre-load in response to the NH₃ pre-load condition; an injector command module configured to provide a NO_(x) reductant injection signal to the reductant injector to inject an amount of reductant into the exhaust stream in response to the first amount of NH₃ pre-load, wherein: the NH ₃ pre-loading module is further configured to determine that the NH₃ pre-load condition for the SCR catalyst in response to at least one of: an ambient temperature being below a cold start threshold; an NH₃ storage amount on the SCR catalyst being below a storage needed threshold; and a current SCR temperature being within an NH₃ storage temperature range.
 8. The apparatus of claim 7, wherein the injector command module is further configured to provide a NO_(x) reductant injection signal in response to the engine being shut down.
 9. The apparatus of claim 7, wherein the NH₃ requirements module is further configured to determine the first amount of NH₃ pre-load by a quantifying operation selected from the quantifying operations consisting of: determining a current available storage capacity of the SCR catalyst at a current SCR catalyst temperature; modeling a final temperature of the SCR catalyst that will be present after an injected urea hydrolyzes into NH₃, and determining a final available storage capacity of the SCR catalyst that will be available at the final temperature of the SCR catalyst; determining an amount of NH₃ selected such that if the engine is cold soaked to a current ambient temperature, enough NO_(x) will be converted by the amount of NH₃ during a subsequent engine start that a threshold amount of NO_(x) will not be emitted downstream of the SCR catalyst during a subsequent engine start before a urea hydrolysis temperature will be reached in the exhaust stream; and determining an amount of NH₃ selected such that if the engine is cold soaked to a current ambient temperature, enough NO_(x) will be converted by a total amount of NH₃ stored on the SCR catalyst during a subsequent engine start that a threshold amount of NO_(x) will not be emitted downstream of the SCR catalyst during a subsequent engine start before a urea hydrolysis temperature will be reached in the exhaust stream, wherein the total amount of NH₃ comprises the amount of NH₃ plus an initially stored amount of NH₃.
 10. The apparatus of claim 7, wherein the controller further comprises an NH₃ scheduling module configured to determine a current NH₃ concentration value, and wherein the injector command module is further configured to provide the NO_(x) reductant injection signal such that an NH₃ concentration value in the exhaust stream does not exceed an NH₃ threshold.
 11. The apparatus of claim 10, wherein the NH₃ threshold comprises one of an emissions limit and an amicability limit.
 12. The apparatus of claim 7, wherein the NH₃ pre-loading module is further configured to determine that the NH₃ pre-load condition for the SCR catalyst is present by determining that an ambient temperature is above a urea hydrolysis threshold.
 13. A system, comprising: an engine fluidly coupled to an exhaust stream; a selective catalytic reduction (SCR) catalyst disposed in the exhaust stream; a NO_(x) reductant injector operationally coupled to the exhaust stream and fluidly coupled to one of an ammonia (NH₃) source and a urea source; a controller operably connected to the NO_(x) reductant injector and configured to: interpret an SCR catalyst temperature and an ambient temperature; determine that an NH₃ pre-load condition for the SCR catalyst is present in response to the ambient temperature and an NH₃ storage amount on the SCR catalyst being below a storage needed threshold; determine a first amount of NH₃ pre-load in response to the NH₃ pre-load condition and the SCR catalyst temperature; and command the injector to inject an amount of urea into the exhaust stream in response to the first amount of NH₃ pre-load.
 14. A system, comprising: an engine fluidly coupled to an exhaust stream; a selective catalytic reduction (SCR) catalyst disposed in the exhaust stream; a NO_(x) reductant injector operationally coupled to the exhaust stream and fluidly coupled to one of an ammonia (NH₃) source and a urea source; a controller operably connected to the NO_(x) reductant injector and configured to: interpret an SCR catalyst temperature and an ambient temperature; determine that an NH₃ pre-load condition for the SCR catalyst is present in response to the ambient temperature and a current SCR temperature being within an NH₃ storage temperature range; determine a first amount of NH₃ pre-load in response to the NH₃ pre-load condition and the SCR catalyst temperature; and command the injector to inject an amount of urea into the exhaust stream in response to the first amount of NH₃ pre-load. 